Mechanics of Ventilation

Question 1

What are the two general classifications of the respiratory system?

Answer 1

Conducting zone

Respiratory zone

Question 2

Which zone has a larger surface area?

Answer 2

Respiratory zone

Question 3

Muscle that accounts for most of inspiratory effort.

Answer 3

Diaphragm

-external intercostals also used in quiet inspiration

Question 4

Two accessory muscles that aid in forced inspiration.

Answer 4

1. Scalenes

2. SCM

Question 5

Muscles used in quiet expiration and then forced expiration.

Answer 5

Quiet: passive
Forced: abdominals and internal intercostals

Question 6

What is Tidal Volume (TV)?

Answer 6

volume of air inspired or expired with each normal breath.

Question 7

What is inspiratory reserve volume (IRV)?

Answer 7

Extra volume of air that can be inspired above normal TV.

Question 8

What is expiratory reserve volume (ERV)?

Answer 8

Maximum extra volume of air that can be expired after the end of a normal TV expiration.

Question 9

What is Residual Volume (RV)?

Answer 9

Volume of air remaining in the lungs after the most forceful expiration.

Question 10

What is Inspiratory Capacity (IC)?

Answer 10

IC = TV + IRV

Question 11

What is Functional Residual Capacity (FRC)?

Answer 11

FRC = ERV + RV

Question 12

What is the Vital Capacity (VC)?

Answer 12

VC = IRV + TV + ERV

Question 13

What is Total Lung Capacity (TLC)?

Answer 13

TLC = VC + RV

Question 14

What is transpulmonary pressure and how is it calculated?

Answer 14

The pressure difference between the alveoli and the intrapleural space.

TPP = Avleolar pressure - intrapleural pressure

Question 15

What is the chest pressure and how is it calculated?

Answer 15

Pressure difference between the compressive force exerted on the chest wall by the outside barometric pressure and the recoil pressure created on the inside wall by the intrapleural pressure.

Chest Wall Pressure = Intrapleural pressure - barometric pressure

Question 16

What is the respiratory system pressure and how is it calculated?

Answer 16

Pressure difference between outside barometric pressure and the alveolar pressure.

RSP = alveolar pressure - barometric pressure

Question 17

What limits elasticity in the lungs (prevents overexpansion)?

Answer 17

Collagen
(elastin contributes to the elasticity and recoil with exhalation but the collagen actually limits the expansion to prevent tearing of the elastin fibers)

Question 18

At what transpulmoary pressure is the lung’s compliance high and when is it low?

Answer 18

Compliance is the change in volume/change in transpulmonary pressure.

At high transpulmonary pressure, the compliance is low mainly because the collagen prevents expansion of the lung tissue.

At low transpulmonary pressure, the compliance is high mainly because the elastic fibers have not been stretched to resist expansion.

Question 19

Why does a saline lung have less hysteresis (difference between inhalation limb and exhalation limb on a lung pressure graph) compared to a normal lung?

Answer 19

Saline filled lungs have less surface tension in the alveoli. The slope in phase 1 of the inhalation limb on the tranpulmonary pressure graph has a low slope due to difficulty overcoming high surface tension in the alveoli, but the slop increases in phase 2 and 3 as the alveoli open and decrease the surface tension.

Question 20

Which alveoli (large or small) have higher surface tension?

Answer 20

Small alveoli have higher surface tension. This means that a larger pressure is required to keep a smaller alveolus open and that, given the option, air will move to a larger alveolus during inspiration.

Question 21

What decreases surface tension in the lungs?

Answer 21

Surfactant: secreted by type II alveolar cells

Pneumocyte Type II

Question 22

What effect does surfactant have on compliance and elasticity of lungs?

Answer 22

Increases compliance: surfactant decreases surface tension which makes alveoli easier to expand with air

Decreases elasticity: surface tension inhibits expansion of alveoli just like elastin fibers, when this is removed the elasticity decreases

Question 23

most important force holding the lungs and chest wall together.

Answer 23

Transmural pressure

-combination of transpulmonary pressure and chest wall pressure

Question 24

What causes the lungs to collapse in a pneumothorax?

Answer 24

Intrapleural pressure increases to zero (zero is designated as outside barometric pressure). This was the main pressure holding the lungs open and the negative pressure becomes more positive revering the force it applies on the lungs.

Question 25

How does the intrapleural pressure vary in the different regions of the lungs?

Answer 25

Lowest in the apex because the alveoli are larger and the alveolar pressure is smaller.
Highest in the base because the alveoli are smaller.

Question 26

How does the compliance vary in the different regions of the lung?

Answer 26

Even though the surface tension is smaller in the apex, the larger alveoli are distended, which stretches the elastin fibers and decreases overall compliance.

Compliance is higher at the base.

Question 27

Biggest factor contributing to airway resistance.

Answer 27

Radius of the airways
-upper airways are the most dilated so air flow can be turbulent. Flow is more laminar in the lower airways.

-when additive cross sectional area is concerned the lower airways have an overall less resistance due to the larger cross sectional area

Question 28

What effect does lung volume have on airway resistance?

Answer 28

Larger volumes expand the airways do resistance decrases.

Question 29

What is the equal pressure point (EPP)?

Answer 29

Point where the transmural (transpulmonary) pressure grandient is zero. Normally it is located in the trachea during quiet breathing. During forced expiration (when intrapleural pressure rises very high) the EPP shifts and moves down to smaller airways. In airways without cartilage, the airways downstream to the flow of air in expiration experience dynamic compression, increased resistance and risk of collapse.

Question 30

Where is the EPP located in patients with emphysema?

Answer 30

Close to the alveoli
-the alveoli lose elasticity so the alveolar pressure is very close to the intrapleural pressure (transmural pressure close to zero)

Question 31

What effect does dynamic compression have on peak expiratory flow rate?q

Answer 31

Regardless of the effort put into the expiration, dynamic compression restricts flow of air and the rate of expiration is the same for all efforts of expiration.

Question 32

What effect do restrictive diseases (fibrosis) have on airway resistance?

Answer 32

No effect on resistance

Question 33

What is forced vital capacity?

Answer 33

FVC is the volume of air that can be forcibly expired from the lungs.

Question 34

How is FVC and forced expiratory volume in one second (FEV-1) influenced by obstructive lung disease and restrictive lung disease?

Answer 34

Obstructive: FVC decreases because the compliance of the lungs is high and elasticity is low. Also dynamic compression occurs preventing air from exiting the airways. FEV-1 also decreases.

Restrictive: FVC decreases because the lungs cannot inspire normal amounts of air and therefore the FEV-1 also decreases.

Question 35

How do the FEV-1/FVC ratios compare in normal lungs vs. obstructive and restrictive disease?

Answer 35

Normal: 80%
Obstructive: smaller (ex. 40%)
Restrictive: higher (ex. 90%)